Surface modification of polyimide membranes by diamines for H₂ and CO₂ separation

The separation of H₂/CO₂ is technologically important to produce the next generation fuel source, hydrogen, from synthesis gas. However, the separation efficiency achieved by polymeric membranes is usually very low because of both unfavourable diffusivity selectivity and solubility selectivity between H₂ and CO₂. A series of novel diamino-modified polyimides has been discovered to enhance the separation capability of polyimide membranes especially for H₂ and CO ₂ separation. Both pure gas and mixed gas tests have been conducted. The ideal H₂/CO₂ selectivity in pure gas tests is 101, which is far superior to other polymeric membranes and is well above the Robeson's upper-bound curve. Mixed gas tests show an ideal selectivity of 42 for the propane-1,3-diamine-modified polyimide. The lower selectivity is a result of the sorption competition between H₂ and the highly condensable CO₂ molecules. However, both pure gas and mixed gas data are better than other polymeric membranes and above the Robeson's upper-bound curve. It is evident that the proposed modification methods can alter the physicochemical structure of polyimide membranes with superior separation performance for H ₂ and CO₂ separation